I want to add that if I install in the Legacy mode of the system, I have not to make any changes after Qubes installation and reboot to boot correctly.
Further explanation: Righ before selecting which device to boot from, you can choose UEFI or Legacy mode. USB device is listed in both sections. I am aware that “Legacy” is also a mode of UEFI according to What's the best: UEFI vs. Legacy? (security-wise) - #4 by Fire